1,566 research outputs found
Computational fluid dynamics challenges for hybrid air vehicle applications
This paper begins by comparing turbulence models for the prediction of hybrid air vehicle (HAV) flows. A 6 : 1 prolate spheroid is employed for validation of the computational fluid dynamics (CFD) method. An analysis of turbulent quantities is presented and the Shear Stress Transport (SST) k-ω model is compared against a k-ω Explicit Algebraic Stress model (EASM) within the unsteady Reynolds-Averaged Navier-Stokes (RANS) framework. Further comparisons involve Scale Adaptative Simulation models and a local transition transport model. The results show that the flow around the vehicle at low pitch angles is sensitive to transition effects. At high pitch angles, the vortices generated on the suction side provide substantial lift augmentation and are better resolved by EASMs. The validated CFD method is employed for the flow around a shape similar to the Airlander aircraft of Hybrid Air Vehicles Ltd. The sensitivity of the transition location to the Reynolds number is demonstrated and the role of each vehicle£s component is analyzed. It was found that the ¦ns contributed the most to increase the lift and drag
Analysis of Hybrid Air Vehicles using Computational Fluid Dynamics
This paper presents an aerodynamic study of bodies related to lighter than air vehicles, using Computational
Fluid Dynamics. The work begins with the validation of the CFD method using a 6:1 prolate
spheroid. The validated method is then employed for the study of the flow around a shape similar to the
Airlander aircraft of Hybrid Air Vehicles Ltd. An overview of the flow around is presented, supported by
pressure survey, flow visualisation and transitional flow effects. The sensitivity of the transition location
to the Reynolds number is also demonstrated, and the role of each component of the vehicle is analysed
in terms of its effect on the flow-field, the lift and drag, and stability in pitch. It was found that the fins
contributed the most to increase the lift and drag coefficients
The impact of psychosis on the course of cognition: a prospective, nested case-control study in individuals at clinical high-risk for psychosis
BACKGROUND: Although cognitive deficits in patients with schizophrenia are rooted early in development, the impact of psychosis on the course of cognitive functioning remains unclear. In this study a nested case-control design was used to examine the relationship between emerging psychosis and the course of cognition in individuals ascertained as clinical high-risk (CHR) who developed psychosis during the study (CHR + T). METHOD: Fifteen CHR + T subjects were administered a neurocognitive battery at baseline and post-psychosis onset (8.04 months, s.d. = 10.26). CHR + T subjects were matched on a case-by-case basis on age, gender, and time to retest with a group of healthy comparison subjects (CNTL, n = 15) and two groups of CHR subjects that did not transition: (1) subjects matched on medication treatment (i.e. antipsychotics and antidepressants) at both baseline and retesting (Meds-matched CHR + NT, n = 15); (2) subjects unmedicated at both assessments (Meds-free CHR + NT, n = 15). RESULTS: At baseline, CHR + T subjects showed large global neurocognitive and intellectual impairments, along with specific impairments in processing speed, verbal memory, sustained attention, and executive function. These impairments persisted after psychosis onset and did not further deteriorate. In contrast, CHR + NT subjects demonstrated stable mild to no impairments in neurocognitive and intellectual performance, independent of medication treatment. CONCLUSIONS: Cognition appears to be impaired prior to the emergence of psychotic symptoms, with no further deterioration associated with the onset of psychosis. Cognitive deficits represent trait risk markers, as opposed to state markers of disease status and may therefore serve as possible predictors of schizophrenia prior to the onset of the full illness
Gene expression patterns in human blood cells exposed to common flu-like viruses and arenavirus
Residual Symmetries in the Presence of an EM Background
The symmetry algebra of a QFT in the presence of an external EM background
(named "residual symmetry") is investigated within a Lie-algebraic, model
independent scheme. Some results previously encountered in the literature are
here extended. In particular we compute the symmetry algebra for a constant EM
background in D=3 and D=4 dimensions. In D= 3 dimensions the residual symmetry
algebra is isomorphic to , with the
centrally extended 2-dimensional Poincar\'e algebra. In D=4 dimension the
generic residual symmetry algebra is given by a seven-dimensional solvable Lie
algebra which is explicitly computed. Residual symmetry algebras are also
computed for specific non-constant EM backgrounds.Comment: 11 pages, Late
Quaternionic and Octonionic Spinors. A Classification
Quaternionic and octonionic realizations of Clifford algebras and spinors are
classified and explicitly constructed in terms of recursive formulas. The most
general free dynamics in arbitrary signature space-times for both quaternionic
and octonionic spinors is presented. In the octonionic case we further provide
a systematic list of results and tables expressing, e.g., the relations of the
octonionic Clifford algebras with the cosets over the Lorentz algebras,
the identities satisfied by the higher-rank antisymmetric octonionic tensors
and so on. Applications of these results range from the classification of
octonionic generalized supersymmetries, the construction of octonionic
superstrings, as well as the investigations concerning the recently discovered
octonionic -superalgebra and its superconformal extension.Comment: 24 pages, LaTe
Psychosis Prevention: A Modified Clinical High Risk Perspective From the Recognition and Prevention (RAP) Program
OBJECTIVE: Early intervention and prevention of psychosis remain a major challenge. Prediction would be greatly advanced with improved ability to identify individuals at true risk, which, at present, is moderate at best. The authors tested a modified strategy to improve prediction by selecting a more homogeneous high-risk sample (attenuated positive symptom criteria only, age range of mid-teens to early 20s) than is currently standard, combined with a systematic selection of neurodevelopmental deficits. METHOD: A sample of 101 treatment-seeking adolescents (mean age, 15.9 years) at clinical high risk for psychosis were followed clinically for up to 5 years (mean follow-up time, 3.0 years, SD=1.6). Adolescents were included only if they exhibited one or more attenuated positive symptoms at moderate to severe, but not psychotic, severity levels. Cox regression was used to derive a risk index. RESULTS: The overall conversion rate to psychosis was 28.3%. The final predictor model, with a positive predictive validity of 81.8%, consisted of four variables: disorganized communication, suspiciousness, verbal memory deficits, and decline in social functioning during follow-up. Significant effects also suggest narrowing the risk age range to 15-22 years. CONCLUSIONS: Clinical high risk criteria that emphasize disorganized communication and suspiciousness while also including compromised verbal memory and declining social functioning have the potential to improve predictive accuracy compared with attenuated positive symptoms used alone. On the resulting risk index (a weighted combination of the predictors), low scores were interpreted as signifying minimal risk, with little treatment necessary, high scores as suggesting aggressive intervention, and intermediate scores, although less informative, as supporting psychosocial treatment
Tailoring Organic-Organic Poly(vinylpyrrolidone) Microparticles and Fibers with Multiwalled Carbon Nanotubes for Reinforced Composites
Polymeric-based microparticles and fibers are tailorable for a wide range of common industrial and biomedical applications, while multiwalled carbon nanotubes (MWCNTs) are among the most useful macromolecules based on their outstanding electronic, mechanical, and optical properties at the nanoscale. If one combines these nanostructures with various polymeric precursors, their range of potential applications becomes even greater. One of the simplest and most affordable methods for fabricating micro- and nanostructures is electrospinning. Herein we demonstrate how MWCNTs may be used to produce tailor-made organic-organic poly(vinylpyrrolidone) (PVP) microparticles and fibers via electrospinning by studying their structural, vibrational, rheological, and mechanical properties' dependence on their solvent (ethanol (EtOH) or dimethylformamide (DMF)) and resulting morphology. Specifically, we find clear differences in morphologies from perfectly spherical and isolated microparticles to fibers mats, or a combination of fibers with entangled beads, with solvent type and concentration. On the basis of our findings, we propose that the mechanism governing the shape and size of the particles is a competition between the solvent's surface tension, dielectric constant, and viscoelastic properties. We show, based on both our experimental results and density functional theory (DFT) calculations, that OH functionalization of the MWCNTs is essential for achieving high PVP coverages and promoting the stability of the resulting PVP/MWCNT nanocomposite. Finally, by fabricating PVP/MWCNT fiber mats, we demonstrate that low concentrations (0.01-0.1 wt %) of MWCNTs led to a qualitative improvement (â250%) in the resulting mechanical properties, i.e., a reinforced composite. These results show how by controlling the solvent's dielectric constant, surface tension, and polymer concentration, one may produce tailor-made polymeric nanomaterials in combination with other organic/inorganic nanoparticles, i.e., silver, gold, or carbon allotropes, for next-generation applications
Supersymmetric Rotating Black Holes and Causality Violation
The geodesics of the rotating extreme black hole in five spacetime dimensions
found by Breckenridge, Myers, Peet and Vafa are Liouville integrable and may be
integrated by additively separating the Hamilton-Jacobi equation. This allows
us to obtain the St\"ackel-Killing tensor. We use these facts to give the
maximal analytic extension of the spacetime and discuss some aspects of its
causal structure. In particular, we exhibit a `repulson'-like behaviour
occuring when there are naked closed timelike curves. In this case we find that
the spacetime is geodesically complete (with respect to causal geodesics) and
free of singularities. When a partial Cauchy surface exists, we show, by
solving the Klein-Gordon equation, that the absorption cross-section for
massless waves at small frequencies is given by the area of the hole. At high
frequencies a dependence on the angular quantum numbers of the wave develops.
We comment on some aspects of `inertial time travel' and argue that such time
machines cannot be constructed by spinning up a black hole with no naked closed
timelike curves.Comment: 36 pages,LaTeX,8 figures;added 1 reference and a few comments;
formula (2.6) corrected; a few changes to section
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